Field
The present disclosure relates generally to communication systems, and more particularly, to a device-to-device (D2D) wireless communications system that enables hybrid automatic repeat request (HARQ) feedback for unicast sidelink communications.
Background
Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). LTE is designed to support mobile broadband access through improved spectral efficiency, lowered costs, and improved services using OFDMA on the downlink, SC-FDMA on the uplink, and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies. One problem with current D2D communications is that there is no physical layer feedback (e.g., HARQ feedback) for unicast sidelink communications. That is, the transmitting user equipment (UE) does not know if the receiving UE receives and/or properly decodes the unicast transmission. Instead, current D2D communications specify that a transmitting UE may send a unicast sidelink communication multiple times to increase the chances that the unicast sidelink communication is received by the receiving UE. By blindly transmitting unicast sidelink communications multiple times, the spectral efficiency and radio resource utilization of the network may be decreased.